The purpose of this grant is to develop a model with broad applications for the study of cell interaction with extracellular matrix. An emerging concept in the matrix-receptor field is that there is redundancy inherent in the integrin-ligand system and this receptor-ligand multiplicity may provide a mechanism by which cells specifically respond to the extracellular matrix. The proposed research will focus on identifying the underlying mechanisms for this receptor-ligand duplication and provide important information on the regulation of cellular behavior by integrin- matrix interactions. We will develop as our model, the binding of the integrin alpha3beta1 to laminin and fibronectin. Alpha3beta1 is representative of the multiplicity associated with many of the known integrins. Specifically, we will localized and delineate the binding sites within laminin and fibronectin for alpha3beta1. In addition, we will characterize the binding sites in alpha3beta1 for both laminin and fibronectin. This work will be done using proteolytic and chemically derived fragments, recombinant polypeptides and synthetic peptides, derived from laminin, fibronectin and alpha3beta1 in solid phase binding assays, affinity chromatography, crosslinking epitope mapping experiments and for monoclonal antibody production. Taken together, these studies will establish the molecular mechanisms underlying alpha3beta1 interaction with laminin and fibronectin. We have recently demonstrated a cell type specific modulation of alpha3beta1 ligand selectivity. This portion of the proposed research will expand on our preliminary findings and identify possible mechanisms for this cell type specific modulation of receptor binding. These investigations will be done using cDNA analysis and immunological approaches. Finally, the proposed studies will identify and characterize other ligands for alpha3beta1. Using alpha3beta1 as an affinity matrix we have isolated a new potential molecule that may be involved in cell-cell binding through alpha3beta1. The proposed work will further characterize this new glycoprotein and explore the possibilities of yet additional ligands for alpha3beta1 interaction. We anticipate that these studies will contribute to our understanding of the mechanisms by which cell selectivity interact with matrix proteins; thus providing insight into the regulation of cellular behavior by the extracellular matrix. Furthermore, an understanding of the significance for such receptor-ligand redundancy will evolve from the proposed research.